The present invention relates generally to fastener-driving tools used to drive fasteners into workpieces, and specifically to pneumatic-powered fastener-driving tools, also referred to as pneumatic tools or pneumatic nailers.
Fastening tools, and particularly those using compressed air as an energy source, incorporate a housing enclosing a cylinder. Slidably mounted within the cylinder is a piston assembly in communication on one side with a supply chamber and a return chamber on the opposite side thereof. The piston assembly includes a piston head and a rigid driver blade that is disposed within the cylinder. A movable valve plunger is oriented above the piston head. In its at-rest position this valve plunger prevents the drive chamber from communicating to the piston assembly and allows an air flow path to atmosphere above the piston assembly. In its actuated state, the valve plunger prevents or blocks the air flow path to atmosphere and allows an air flow path to the drive chamber
When a tool's actuation requirements have been met, the movable valve plunger opens and exposes one side of the piston assembly to a compressed gas energy source. The resulting pressure differential causes the piston and driver blade to be actuated downward to impact a positioned fastener and drive it into a workpiece. Fasteners are fed into the nosepiece from a supply assembly, such as a magazine, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
As the piston is actuated downward, it drives the air inside the cylinder through a series of vents into the return chamber increasing the pressure in this chamber. After the fastening event has taken place, the valve plunger moves back to the at-rest position, blocking the supply chamber's air flow path to the piston head and releasing the pressure above the piston head through the path to atmosphere. At this time, the pressure built in the return chamber pushes the piston assembly back up towards the top of the cylinder. The air above the piston head is forced through the valve plunger's air flow path to atmosphere.
The pressure available to drive the piston in pneumatic fastening tools varies based on the source. The variance in pressure causes fasteners to be driven to different depths in an underlying substrate or workpiece. Furthermore, the repeated, reciprocal motion of the piston and impact at the bottom of the cylinder reduces the working life of the tool.